Intensive physical training induces NET release in athletes.

The aim of this study was to determine the effect of intense physical training on the release of neutrophil extracellular traps (NETs) in URTI-free and URTI-prone athletes. Sixteen young male ice hockey players were monitored during a national training camp. Blood collection took place at the beginning and after the training camp. Blood tests included creatine kinase activity; white blood cell count and subpopulations; cortisol, immunoglobulin A and C-reactive protein concentrations; and the percentage of neutrophils releasing NETs. The occurrence of upper respiratory tract infections (URTI) was monitored using a validated URTI symptom questionnaire. There were no differences in immune and endocrine markers between URTI-free and URTI-prone athletes. Regardless of the subject's health status, CK activity and uric acid levels increased significantly between the beginning and after the training camp. In both URTI-free and URTI-prone athletes, the percentage of neutrophils releasing NETs increased significantly after the training camp. Regardless of the athlete's health status, a short period of intensive physical training itself may cause increased NET release in ice hockey players. The presence of mild URTI did not appear to be an additional factor influencing NET release during the several-day training camp.